Radioactive diamond and process for the preparation thereof



M y 1965 R. H. WENTORF, JR 3, 1,

RADIOACTIVE DIAMOND AND PROCESS FOR THE PREPARATION THEREOF Filed Feb.28. 1961 zv/crrsz E/VD o/s/r N/C/(EL rues S? GkAPH/TE E PYROPl/VL ure-Tues HEATER SAMPLE/901.051?

M? \ga- RAO/OACT/VE "1f CWRBON an more Ek AL UMNA 7,085 lV/C/(ELEll/flD/Jk AL UM/IVA s/va PLUG- [h vs r7 70 7-.- Robert H Went'or'f J21,

is Attorney.

United States Patent 3,181,933 RADIQACTIVE DEAMQND AND PRO'CESS F63 THEPREPARATEQN THEREGF Robert H. Wentorf, J12, Schenectady, N.Y., assignorto GeneralEleetrie Company, a corporation of New York Filed Feb. 28,196i, Ser. No. 92,357 Claims. (Cl. 23-=-29.l)

This invention relates to radioactive diamond material and to. thepreparation thereof. More particularly, this invention is concerned withdiamonds having a radioactivity extending through the diamond matrix aswell as being present on the surface thereof obtained by heating atelevated temperatures and pressures in the diamond-forming region aradioactive carbonaceous material in combination with a catalyst formaking diamonds.

As is Well known in the art, natural diamonds, particularly naturaldiamonds of the industrial variety, readily acquire and retain a chargeof static electricity. This generally occurs when natural industrialdiamonds come into contact with each other or with some other surface.The static charge on industrial diamonds results in a number of problemsin their use. Thus, when an attempt is made to sort industrial diamonds,it is found that the static charge seriously interferes with thesegregation of the diamonds into various size groups and interferes withthe moving of the diamonds from one location to another. In addition,when natural diamonds are employed in bearings or in grinding tools, thecharge on the surface of the diamond tends to attract dust or otherundesirable particles of matter to the surface of the diamond. Whendiamonds are used as bearing materials such as in timepieces and otherdelicate mechanisms the dust or other particles attracted by the staticcharge by the bearing and, therefore, reduces or destroy the efiicie'ncyof the bearing. Where diamonds are used in industrial grinding tools, itis found that the static charge on the diamond surface causes particlesof dust and of metal to adhere to the surface of the diamond andinterfere with proper and accurate grinding.

One method for making radioactive diamonds is disclosed and claimed inmy copending application Serial No. 562,585, filed January 31, 1956, andassigned to the same assignee as the present invention, now US. Patent2,996,763, issued August 22, 1961. In accordance with this method,diamonds having radioactivity are prepared by heating at elevatedtemperatures and pressures, a mixture comprising a carbonaceou material,for instance, a non-diamond form or carbon, in the presence of aradioactive material, preferably a radioactive metal, and in the furtherpresence of a metal of the type capable of forming diamond from thecarbonaceous material. It was found that when employing a radioactivemetal for making the above-described radioactive diamonds, theradioactivity appeared only on the surface layer of the diamond andapparently was not present in the core of the diamond. For manyapplications this may be sufiicient, but in a large number ofapplications, particularly Where testing of abrasives is important todetermine the efficiency of the abrasive, there is a need for theradioactivity to be not only on the surface layer but also to be presentin the matrix of the diamond and advantageously permeate the entirediamond.

Unexpectedly, I have discovered that I am able to make radioactivediamonds in which the radioactivity of the diamonds extends throughoutthe entire diamond, including the surface layer and matrix thereof,subjecting a radioactive carbonaceous material, such a radioactivenon-diamond carbon, to elevated temperatures and pressures in thediamond-forming region in the presence Patented May 4-, 1&65

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of a metal or alloy conducive to the formulation of diamonds.

It is accordingly an object of the present invention to provide adiamond material which does not retain a charge of static electricity ofany substantial period of time.

Another object of the present invention is to prepare diamond materialof the type described having a radioactivity exceeding that of knowndiamond from a radioactive carbonaceous material such as radioactivenondiamond carbon.

It is a further object of the present invention to provide a radioactivediamond whose radioactivity is present not only on the surface layerthereof, but also permeates the entire matrix of the diamond as a resultof radioactive carbon atoms introduced during production thereof.

The term radioactive carbonaceous material is used in the presentapplication to refer to a carbonaceous material, for instance,non-diamond carbon, such as graphite, which has the property ofspontaneously emitting alpha, beta, or gamma rays, or neutrons by thedisintegration of the nuclei of the atoms of the carbonaceous material.As is well known, the radiation emitted by radioactive elements causesionization of the medium surrounding in the radioactive material or themedium through which the alpha, beta, gamma rays, or neutrons pass. Itis further understood that when, for example, air is ionized by raysfrom a radioactive material, the ionized air becomes, to some extent, aconductor of electricity. Thus, Where the diamond material of thepresent invention acquires a static charge, the radioactivity of thediamond material causes ionization of the air or other mediumsurrounding'the diamond material and this ionized air or other mediumcarries away the static charge from the surface of the diamond material,rendering the diamond material electrically neutral.

As can be seen from the description of the ionization of the mediumsurrounding the diamond materials of the present invention and thedischarging of the static charge on the diamond material, the diamondmaterial of the present invention is free from the problems associatedwith natural diamonds. Thus, since the diamonds of the present inventiondo not retain a static charge, they may be sorted without the difficultycaused by any static charge on the material. In addition, when thediamonds of the present invention are used as bearings, they will haveno tendency to attract dust or other abrasive particles to theirsurface. Furthermore, when the diamond material of the present inventionis employed as abrasive material in abrasive wheels, there is again notendency for any static charge to accumulate on the diamonds andtherefore there is no tendency for the grinding wheel to attractparticles of metal which may interfere with the accurate use of thegrinding wheel.

Various catalysts may be employed in the preparation of the radioactivediamonds of the present invention. Generally, these catalysts comprisemetals or alloys of metals which have been found to besignificantlyeifective in converting carbonaceous materials to diamond. Includedamong the metals which may be employed as a catalyst for making theradioactive diamonds may be 7 mentioned, for instance, iron, cobalt,nickel, rhodium,

of converting the carbonaceous material to diamond. lneluded among suchalloys may be alloys of metals selected from the class consisting of theabove metals, many examples of such alloys being given in Strong Patent2,947,- 609, issued August 2, 1960.

The pressure at which the radioactive diamonds may be made will dependupon various considerations, such as temperature, the particularradioactive carbonaceous material which may be used, the catalystemployed, and whether the catalyst and alloy are individual metal, etc.Since it is known that the measurement of pressures in the high rangesrequired for making diamonds is relatively difilcult, it will beapparent that no exact standard for effecting these measurements can bestated. However, prior art workers have attempted to rely on suchpressure measurements by determining the phase changes which occur insuch metals as bismuth, thallium, cesium, and barium. If one employs asstandards the phase changes which result in these metals bydetermination of changes of electrical resistance, it will be found thatpressures on the order of from 40,000 to 100,000 atmospheres or moreordinarily are found to be the range of pressure useful in making of thediamonds in the present invention. Regardless of the standards which areused for measuring the pressures under which the radioactivecarbonaceous material undergoes transformation to diamond, the pressurerange will be within the limits recited above and advantageously withinthe range of about 42,000 to about 75,000 atmospheres.

The temperatures at which diamonds of the present invention may beformed can also be varied widely in accordancewith the factors whichwill cause variation in the pressures. the range of about 1200 C.toabout 2200 C. or higher. Caution should be exercised that in makingdiamonds, the actual temperature and pressure is that required foroperating within the diamond-forming region and that any changes oftemperature or pressure will not be used which in any Way adverselyaffect the desired result.

The process of the present invention may be carried out in any type ofapparatus capable of producing the pressures required at the temperaturerequired. However, I prefer to employ apparatus of the type described inthe patent of H. T. Hall, US. 2,941,248, issued June 21, 1960, andassigned to the same assignee as the present invention. The apparatusdisclosed in the aforementioned Hall patent is a high pressure devicefor insertion between the platens of a hydraulic press. The highpressure device consists of an annular member defining a substantiallycylindrical reaction area, and two conical, piston-type members designedto fit into the substantially cylindrical portion of the annular memberfrom either side of said annular member. A reaction vessel which fitsinto the annular member may be compressed by the two piston members toreach the pressures required in the practice of the present invention.The temperature required is obtained by any suitable means, such as, forexample, by induction heating, by passing an electrical current throughthe reaction vessel, or by winding heating coils around the reactionvessel.

The reaction vessel or cylinder described in the above Hall patent maybe formed of any of the conventional materials of construction or ofgraphite. Where the reaction vessel is constructed of a metal, it isconvenient to employ one of the metals which acts as a catalyst in thepresent invention. This vessel may then be filled with the radioactivenon-diamond carbon and compressed so that the metal present in thevessel will serve as a catalyst for the transformation to diamond. Wherethe reaction chamber or vessel is formed of radioactive graphite, it maybe filled with the catalyst material and the compression of the graphitevessel with the catalyst at the pressures and temperatures required bythe present invention results in the transformation of the radioactivenon-diamond carbon into the radioactive diamond of the Generally, Iemploy temperatures within &

present invention. Regardless of the material of construction of thereaction vessel, the radioactive non-diamond carbon and the catalyst maybe admixed inside the vessel. Thus, mixtures of powdered radioactivegraphite and powdered catalyst may be employed as a charge in thereaction vessel and the compression of the vessel and charge at therequired temperature effects transformation to radioactive diamondmaterial.

In the preferred embodiment of my invention, l employ a reaction vesselcomprising a cylinder of graphite (which may or may not be radioactive)having a hollowedout cylindrical center portion, the axis of the centerportion being coaxial with the axis of the reaction vessel. Into thisgraphite reaction vessel are placed cylinders or disks of radioactivegraphite and the catalyst. This reaction vessel is sealed at its end bymetallic disks which may be formed of any material of construction inertunder the conditions of the reaction or it may be formed of a catalystmetal. This reaction vessel is then placed in the apparatus described inthe above-mentioned Hall patent and subjected to the elevatedtemperature and pressure required to effect the transformation toradioactive diamond material. Alternatively, instead of employing areaction vessel, a cylinder of radioactive carbonaceous material, suchas radioactive graphite, may be sandwiched between two disks formed of ametal which acts as a catalyst for the transformation. The sandwich isthen placed in the high pressure apparatus and subjected to theconditions required to cause the transformation to radioactive diamondmaterial. As a further alternative, a metallic reaction vessel may befilled with a radioactive carbonaceous material in powder or solid formand the catalyst for the reactionmay be supplied by admixing it with thepowdered radioactive carbonaceous material or by forming end disks ofeither of the catalyst materials to seal the reaction vessel. Thisassembly is then subjected to the pressures and temperatures required. Areaction vessel may also be formed by compressing a mixture ofradioactive non-diamond carbon and catalyst until a cylinder is formedwhich fits into the substantially cylindrical aperture described in theabove-mentioned Hall patent.

Again, this latter apparatus may be employed in the usual manner atelevated temperatures and pressures to effect the transformation toradioactive diamond material.

The annexed drawing illustrates a preferred embodiment of the invention.

In carrying out the process of the present invention, the temperature inthe reaction vessel may be measured by a thermocouple located adjacentthe reaction vessel previously mentioned. In carrying out this process,the time of reaction required to convert the reaction mixture intoradioactive diamond material may vary from a few seconds up to severalminutes or more depending on the particular charge to the reactionvessel. However, regardless of the charge to the reaction vessel, I havefound that the radioactive diamond material of the present invention isformed within two to seven minutes. instead of observing the time whichthe reaction vessel is maintained at the reaction temperature, I mayalternatively observe the progress of the reaction by the methoddescribed in the patent of H. T. Hall, U.S. 2,947,608, issued August 2,1960, and assigned to the same assignee as the present invention. By theprocess of this Hall patent, the mixture of radioactive non-diamondcarbon and catalyst is first subjected to a pressure of at least about40,000 to 60,000 atmospheres (depending on the catalyst used) andsubsequently sufiicient heat is applied to the mixture for a suflicienttime to cause an inflection in the electrical resistance of the mixture.When the inflection in the electrical resistance of the mixture occurs,the transformation of the mixture to the radioactive diamond material ofthe present invention has begun to occur.

The radioactive carbonaceous materialswhich may be employed in thepractice of the present invention include all of the man-producedradioactive isotopes of carbonaceous materials, such as carbon 14,radioactive graphite (made radioactive by bombardment, for instance, inan atomic reactor, with neutrons, with energetic particles or with highenergy radiation).

In preparing the radioactive diamond material of the present invention,the proportions of the ingredients employed are not critical, and I havefound that suitable radioactive diamond material can be formedregardless of the relative concentrations of the radioactive non-diamondcarbon and the catalyst. The presence of nonradioactive carbonaceousmaterial is not precluded as long as the amount of such material doesnot adversely affect obtaining the radioactive diamond. In the preferredembodiment of this invention, it is preferred to have the ingredientspresent, on a weight basis, in the proportions of about 0.1 to parts ormore of catalyst per part of radioactive non-diamond carbon. Regardlessof the proportions of ingredients and the physical location of thevarious ingredients in the reaction vessel, it has been found that theresulting product comprises diamond having a radioactivity extendingthroughout its mass as well as on its surface.

Since the radioactive materials of the present invention are similar toother radioactive materials, some degree of care is necessary inhandling the products of the present invention. The degree of carerequired in handling the radioactive diamond materials is similar tothat degree required in handling the radioactive corbonaceous materialitself.

The following examples are illustrative of the practice of my inventionand are not intended for purposes of limitation.

Example 1 In this example, a solid cylinder of radioactive graphite(machined from a block of graphite which had been made radioactive bybeing subjected to the radiation flux in an atomic pile at Oak Ridge,Tennessee, US. Atomic Installation) 0.295 inch in diameter and 0.75 inchlong, was encased in a thin walled nickel tube (as catalyst) which wasin turn encased in an alumina insulating sheath which was enclosed in acarbon tube heater. This assembly, which is more particularlyillustrated in the attached drawing, was placed in the usualpyrophyllite sample holder as shown in the above-mentioned Hall Patent2,941,248, and subjected to a pressure of about 65,000 to 75,000atmospheres at a temperature of about 1500 C. for 27 minutes. Thecapsule was cooled, and removed from the press. Excess carbon and nickelwere dissolved from the pressed slug by the use of hot sulfuric acid towhich KNO had been added, and thereafter the mass was dissolved in aquaregia leaving behind crystals of diamondwhich were identified as such bytheir refractive index and cubic or octahedral crystal habit. Theradioactive diamonds thus obtained were tested for radioactivity (bymeasurement with a Geiger counter) and found to be radioactive not onlyon their surface but also throughout the mass of the diamonds. Most ofthe radioactivity was in the form of gamma rays. Repeated treatmentswith acids did not diminish the radioactivity. This established clearlythat the radioactivity was being released from inside the diamonds. Evenwhen the diamonds were crushed to a powder, the radioactivity couldreadily be determined throughout the powdered mass.

Example 2 0.45 inch. Into this tube was charged a mixture of radioactivegraphite powder (made from the same source as used in Example 1 and thepowder was confined within the tube by end plugs made of an alloy ofnickel and chromium (80 percent nickel and 20 percent chromium) having adiameter of-0.09 inch and about 0.125 inch in height. Thesenickel-chromium alloy plugs were the catalyst for conversion of theradioactive graphite to diamond. The capsule was pressed at a pressureof about 55,000 to 56,000 atmospheres at a temperature between 1250 to1350 C. for about 6 minutes. The slug thus obtained was dissolved inacids and cleaned up similarly as was done in Example 1 to yield a goodquantity of diamonds which exhibited a perceptable degree ofradioactivity. Employing a scintillation counter, it was found that thebackground average was about 257 counts per minute while the diamondplus background average was about 382 counts per minute.

Although the catalyst materials which may be employed in the practice ofthe present invention have been described only in terms of pure metals,or alloys of these metals, it should be understood that compounds ofthese metals which decompose under the conditions of the reaction mayalso be employed. Thus, compounds of the catalyst which decompose intopure metal under the condition of the reaction include, for example, thecarbides, sulfides, carbonyls, cyanides, ferrotungstates,ferritungstates, oxides, nitrides, nitrates, hydrides, chlorides, molybdates, arsenates, acetates, oxalates, carbonates, borates, chromates,phosphates, phosphides, permanganates, silicates sulfates, tungstates,etc. Specific examples of decomposable compounds usable as catalysts inthe present invention include ferrous sulfide, iron carbonyls, palladiumchloride, chromium carbide, tantalum hydride, sodium fluoride, nickelpermanganate, cobalt acetate, nickel sulfate, etc. Obviously othercatalysts, both metal and alloy may be employed, many examples of whichhave been given above, without departing from the scope of theinvention.

Although the above examples have described the reaction of the presentinvention only at certain pressures and temperatures, it should beunderstood that any pressure in excess of 40,000 atmospheres issatisfactory for the practice of this invention. My preferred pressurerange is from about 46,000 to 85,000 atmospheres. Similarly, mytemperature range may vary from 1200 C. to 2000 C., and preferably fromabout 1400 C. to 1800 C. Other examples of catalyst, temperature, andpressure which may be employed can be found in the foregoing US. Patents2,947,610, 2,947,609, and 2,947,611.

The radioactive diamond material or" the present invention is useful forall of those uses to which diamonds are commonly put. In addition, thisradioactive diamond material is particularly useful as the abrasivemedium in an abrasive wheel. In addition, the radioactive diamondmaterial of the present invention is particularly suitable for use as abearing surface in applications where the bearing must withstand anextremely high load and where the dust which would be attracted by anordinary diamond bearing would ruin the effectiveness of the bearingaction. Thus, the radioactive diamond materials of the present inventionare particularly suitable as jewels for use in clocks, timers, and thelike where dust might interfere with the accuracy of the device.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A process for making man-produced radioactive diamonds having aradioactivity which is both (1) coextensive with the mass of the diamondand (2) exceeds that of known diamond, which process comprises heatingat a temperature in excess of 1200 C. and at a pressure in excess of40,000 atmospheres in the diamond-forming region, a man-producedcarbonaceous material rendered radioactive by bombardment with highenergy radiation in combination with a catalyst for diamond formation.

2. The process as in claim 1 in which the man-produced radioactiveisotope is graphite made radioactive by subjectingthe graphite to theradiation flux in an atomic pile.

- 3. The process as in claim 1 in which the catalyst is an alloy ofnickel and chromium.

4. The process as in claim 1 in which the catalyst is nickel.

5. Man-produced diamond having a radioactivity both on its surface andthroughout its mass in which radioactive carbon atoms have beenintroduced during the production of said diamond, the said radioactivitybeing substantiaily greater than that of known diamond.

References Cited by the Examiner UNETED STATES PATENTS 2,315,845 4/43Ferris 252301.1

0 3 2,947,610 8/60 Ha1ieta1. 23- 209.1

FOREIGN PATENTS 1,009,251 3/52 France.

5 OTHER REFERENCES Freedman: J. Chem. Physics, 20, 1040 (1952).Bradford: Radioisotopes in Industry, pp. 24, 84, 279, Reinhold Publ.Co., N.Y., 1953.

10 MAURICE A. BRINDISI, Primary Examiner.

1. A PROCESS FOR MAKING MAN-PRODUCED RADIOACTIVE DIAMONDS HAVING ARADIOACTIVITY WHICH IS BOTH (1) COEXTENSIVE WITH THE MASS OF THE DIAMONDAND (2) EXCEEDS THAT OF KNOWN DIAMOND, WHICH PROCESS COMPRISES HEATINGAT A TEMPERATURE IN EXCESS OF 1200*C. AND AT A PRESSURE IN EXCESS OF40,000 ATMOSPHERES IN THE DIAMOND-FORMING REGION, A MAN-PRODUCEDCARBONACEOUS MATERIAL RENDERED RADIOACTIVE BY BOMBARDMENT WITH HIGHENERGY RADIATION IN COMBINATION WITH A CATALYST FOR DIAMOND FORMATION.